--- /home/ml213213/git/ext/org-mode/lisp/org-bibtex.el	2013-01-28 13:28:21.910313351 +0100
+++ /home/ml213213/.emacs.d/elpa/org-plus-contrib-20121231/org-bibtex.el	2013-01-28 13:23:26.786308753 +0100
@@ -708,7 +679,7 @@
         (org-agenda-search-view-always-boolean t))
     (org-search-view nil
 		     (format "%s +{:%s%s:}"
-			     string org-bibtex-prefix
+			     string (or org-bibtex-prefix "")
 			     org-bibtex-type-property-name))))
 
 (provide 'org-bibtex)